1. Technical Field
The present invention relates to a display device.
2. Related Art
In general, an electrophoretic display device (EPD) is well known as an example of display devices. For example, an electrophoretic display device including a display portion having a structure in which the space between a pair of substrates is partitioned into a plurality of spaces by partitioning walls, and a solvent in which particles having chargeability and dispersibility are injected (this solvent being referred to as a dispersion liquid hereinafter) is sealed in each of the plurality of spaces is well known. Here, the partitioning wall is produced from, for example, an insulation material.
Such an electrophoretic display device is capable of changing the content of display of the display portion by allowing a voltage to be applied to the dispersion liquid sealed in each of the spaces and sandwiched between two electrodes so as to cause two groups of particles constituting the particles, the color (displayed color) and the reflectance of particles constituting one of the two groups being different from those of particles constituting the other one of the two groups, to be each separated and moved toward a corresponding one of the two electrodes that is specified by the applied voltage. For example, a white and black display portion using two kinds of particles, one being associated with a white color (this kind of particles being referred to as “white particles”), the other one being associated with a black color (this kind of particles being referred to as “black particles”), allows the white color to be displayed through the use of light scattering of the white particles, and allows the black color to be displayed through the use of light absorption of the black particles.
Such an electrophoretic display device is constituted as, for example, a reflection type display device configured to obtain the contrast of display through the use of the reflection of outside light. In this case, the electrophoretic display device includes a light guiding plate disposed so as to be stacked and a light source, such as a front light, for illuminating a display face, taking it account a case where the electrophoretic display device is used at a dark place at night or the like. This configuration is similar to that of commercially produced electrophoretic display devices.
When a front light based illumination structure is used in a reflection type display unit, a configuration in which a light guiding plate is disposed at a position on a display face to allow light from a light source disposed at a side face of the light guiding plate to enter the light guiding plate is employed.
In the electrophoretic display device, there exists a driven area the periphery of which is enclosed by partitioning walls and in which a dispersion liquid is injected. This driven area is, for example, an area adjacent to which electrodes that supply a voltage to the dispersion liquid exist. Meanwhile, in the electrophoretic display device, there exists a non-driven area the periphery of which is enclosed by partitioning walls and in which a dispersion liquid is injected. This non-driven area is, for example, an area adjacent to which any electrode that supplies a voltage to the dispersion liquid does not exist.
With this configuration, the dispersion liquid injected in the non-driven area is unlikely to be influenced by the voltage, as compared with the dispersion liquid injected in the driven area. That is, the particles included in the dispersion liquid injected in the non-driven area are slow in their movements upon supply of the voltage, as compared with the particles included in the dispersion liquid injected in the driven area. Specifically, the display of the non-driven area is likely to become a gray color (for example, a color resulting from an uneven mixture of white and black), that is, an intermediate color between white and black. The display of the non-driven area is a display that is not intended to be viewed by a user.
As an example of such an electrophoretic display device, an electrophoretic device is disclosed in JP-A-2015-18060 (this electrophoretic device being understood to be equivalent to the electrophoretic display device). This electrophoretic device is provided with an electrophoretic layer including a dispersion medium and partitioned into a plurality of cells by partitioning walls, a frame-shaped partitioning wall disposed at the periphery of the electrophoretic layer in a plan view, and a liquid reservoir disposed between the electrophoretic layer and the frame-shaped partitioning wall in a plan view (this liquid reservoir being understood to be equivalent to the non-driven area) (see JP-A-2015-18060).
In such an electrophoretic display device, there has been a disadvantage in that the non-driven area is easy to be viewed by a user. The non-driven area is not intended to be viewed by a user, and thus, such a configuration that allows a user to view the non-driven area degrades the quality of display.
Such a disadvantage is significant particularly in a configuration in which the light guiding plate is provided in the electrophoretic display device. That is, in a configuration in which the light guiding plate is stacked on the substrate of the electrophoretic display device, the distance between the chassis and the display portion of the electrophoretic display device is increased by the thickness of the light guiding plate, and this increase of the distance between the chassis and the display portion increases a range that allows a user to view the non-driven area.
This disadvantage will be described in detail.
That is, because of an upper electrode substrate that is transparent and is disposed at a position on the dispersion liquid, a display face (the surface of the dispersion liquid) is located at a position distanced from the display frame of the chassis by the thickness of the upper electrode substrate. Thus, viewing of the display face from an oblique direction results in viewing of the boundary between the driven area and the non-driven area, and as a result, this configuration significantly degrades the quality of display.
Particularly, with respect to the front light in the reflection type display, in order to allow the entire display face to be evenly illuminated by light, a configuration that allows the light guiding plate to be disposed at a position on the display face and allows light from the light source, which is disposed at a side face of the light guiding plate, to enter the light guiding plate is typically employed. Here, when a front light based light guiding plate is disposed in a display panel (an EPD panel), the display face is located at a position further distanced from the display frame, and this configuration allows the boundary to be more easily viewed. Further, in a state in which the front light is tuned on, the light is illuminated on the dispersion liquid in the driven area and the dispersion liquid in the non-driven area, and thus, the boundary is easily viewed, as compared with a state in which the front light is turned off. As a result, the quality of display is significantly degraded.